After five years of planning and eight weeks facing extreme exposure and daunting technical hurdles, a local team of oceanographers have returned from Antarctica triumphant in the completion of their mission.

The Naval Postgraduate School oceanographers drilled through 500 meters of glacial ice jutting out into sea off western Antarctica and implanted probes to spy on the interactions between the warming ocean and the melting glacier.

Signals from the probes will aid in predicting global rise in sea level, which is expected to increase as more glacial ice melts into the ocean.

Scientists from NPS, NASA, Pennsylvania State University and the University of Alaska all played a part in the ambitious, multimillion-dollar project.

Opening the floodgates

The researchers set up shop on the Pine Island Glacier. With flows of up to 10,000 feet per year, it's the fastest moving ice shelf in Antarctica. It protrudes 37 miles into the Amundsen Sea from mainland Antarctica, creating a dark oceanic cavern beneath. The secret behavior of sea currents beneath the ice shelf hold the key to predicting how fast it could melt, researchers say.

"There's a surprisingly large number of questions that are completely unknown," said NPS oceanographer Tim Stanton, a leader of the expedition. "How is the ocean interacting with the ice? How is it controlling the flow of heat into the ocean cavity underneath the ice? When it gets under there, how does it melt the ice?"

While the team is measuring the melting characteristics of the Pine Island Glacier, its real concern is about the much larger, land-bound ice sheet — the West Antarctic Ice Sheet (WAIS) — pushing on it from behind.

WAIS covers the western portion of Antarctica — a region roughly half the size of the continental United States. As the Pine Island Glacier melts due to warming oceans, scientists fear that the floodgates could open up, allowing portions of the West Antarctic Ice Sheet to move from the land into the ocean.

Such an event, if it happened, could lead to global sea level rise on the order of several meters, according to William Shaw, another NPS oceanographer who took part in the expedition.

"Imagine a bunch of kids on a slide," he said. "One kid goes down, but doesn't get off. He's just stuck there. Other kids start to slide down, but get stuck on the slide."

The melting ice shelf is equivalent to the bottom kid getting off the slide.

The extent to which WAIS crumbles into the sea depends largely on Pine Island Glacier's melting pace, which is driven by warm ocean currents swirling underneath the shelf. The complex ocean dynamics below such a glacier have never been studied in full detail, Stanton said.

Although Pine Island Glacier isn't the largest ice shelf in Antarctica, its acceleration makes it a prime suspect for sea-level rise. "Ultimately, the Pine Island system is the largest Antarctic contribution to sea level rise," said glaciologist Kelly Brunt, who was not involved in the expedition. "So by studying this one system, the results will still tell us more about the contributions from Antarctica to global mean sea level rise."

Studying this smaller glacier could lend insights into the way other glaciers will behave in the future, according to Shaw. "The Pine Island Glacier is changing rapidly right now, and if we can understand why that glacier's changing, it will improve our chances of predicting more widespread changes," said Shaw.

'Wild place' for science

The NPS team used a hot-water drill to access the salty ocean 500 meters through the glacial ice. Their instruments — which measure water currents, temperature and salinity — had to be custom-built to fit down a bore hole that's 20 centimeters across. Building the novel gadgetry was only one of many challenges the team faced.

"It's a rough and wild place to do an experiment," Stanton said.

At about 1,800 miles from the nearest station, the Pine Island Glacier is a remote region of the already-remote Antarctic continent. The portions of the ice shelf closest to land are full of treacherous crevices, formed by the buckling of the ice shelf under the weight of the massive land-bound ice sheet.

When the team started planning the mission five years ago, they deemed it impossible to land a plane on the ice sheet. At the time, the researchers decided to use helicopters instead — a far more difficult task given their limited range.

Last year, the team waited anxiously at McMurdo Station (the U.S. base in Antarctica) for weeks, but the helicopters were unable to fly in the poor conditions. "We had a disastrous year," Stanton said. "It was so disappointing."

Fed up with waiting and running out of time, team members finally decided to try their luck at landing Twin Otter planes onto the ice shelf. The risky move paid off.

"We proved right at the end of last year that we could land the Twin Otters," Stanton said.

The team only had enough time to drop some of its supplies on the glacier last year, where the equipment sat on the ice awaiting the researchers' return.

Bringing it all together

This year, the team hit the ice running. They flew the Twin Otters out to the Pine Island Glacier where they set up three drill sites. They used two snow machines to lug 18,000 pounds of equipment between camps — totaling an arduous 20 to 30 trips per move.

The oceanographers from NPS worked in concert with glaciologists from Penn State, who used "seismic reflection" to map out the structure of the glacier and the depth of the water below. "We set off small explosives on the surface, and listen for the echoes of that sound off the bottom of the ice, the water and any sediments that are there," said Penn State glaciologist Sridhar Anandakrishnan.

According to Anandakrishnan, a collaborative effort between glaciologists and oceanographers is crucial to discover how ice shelf melting will contribute to sea level rise.

"Until now, the glaciologists have done their thing and the oceanographers have done their thing," he said. "Integrative studies like this one are absolutely critical."

The drilling team took between one and three days to reach the ocean at each site, then lowered equipment to measure the ocean currents, water temperature and melt rates of the ice below. The equipment measures the water temperature to an accuracy of one ten-thousandth of a degree, Stanton said.

Warm river beneath

Their initial measurements revealed a warm water current, called a "boundary layer," flowing along the surface of the ice.

"Right under the ice, you see this boundary layer current," explained Stanton. "What we don't know, is how big is the boundary layer? How big is the current?"

The flow of this relatively warm current will dictate the melt rate of the glacier. To get an accurate assessment of the current, the team's equipment — powered by lithium batteries, a wind generator, and solar panels — will stay in place and send back data for at least the next two years. Eventually, the equipment will reach the tip of the glacier (which moves at about 10,000 feet per year into the sea), and fall into the ocean.

When asked whether they'll return to retrieve their equipment before it falls into the sea, Shaw and Stanton responded without hesitation, "There's no going back."